1. Field of the Invention
The present invention relates to a semiconductor device and a method of producing the semiconductor device, in particular, a method of producing a semiconductor device having a polymetal wiring made of a polycrystalline silicon, an reaction preventing film, and a polymetal wire made of tungsten, especially used for forming highly heat-resistant wire such as a gate electrode.
2. Discussion of Background
In recent years, in accordance with microminiaturization, high integration, and high speed of semiconductor devices, a development of wiring materials having a further small resistance is required. As a wiring material used at portions requiring heat resistance, e.g. a gate electrode of a transistor, instead of a polycide structure fabricated by a polycrystalline silicon film and a metallic silicide film having a high-melting point, a tungsten film being one of high-melting point metals, a polycrystalline silicon film, or polymetal wiring made of a silicide reaction preventing film including a tungsten film and a polycrystalline silicon film. This is because the polymetal wiring using the tungsten film is hoped as wiring having a low sheet resistance in comparison with polycide wiring without an increment of the height of a gate.
FIGS. 11a through 13 are cross-sectional views illustrating steps of a method of producing a conventional p-type MOS transistor having a gate electrode made of polymetal wiring. As illustrated in FIG. 11a, an element isolation insulating film 2 is formed on a silicon substrate 1 to separate an element forming region.
In the next, as illustrated in FIG. 11b, a gate oxide film 3 is formed on an entire surface of the silicon substrate 1.
In the next, as illustrated in FIG. 11c, a polycrystalline silicon film 4 is formed on an entire surface, and BF2 is subjected to ion implantation to form gate wiring of a p-type.
In the next, as illustrated in FIG. 11d, a titanium nitride film 5 is formed on an entire surface of the polycrystalline silicon film 4 by a reactive sputtering method using a metallic target such as Ti. This titanium nitride 5 is served as a reaction preventing film preventing a reaction between the polycrystalline silicon film 4 and a tungsten film to be formed later.
In the next, as illustrated in FIG. 11e, the tungsten film 6 is formed on an entire surface of the titanium nitride film 5 by a CVD method reducing tungsten hexafluoride by monosilane and hydrogen.
As illustrated in FIG. 12a, thee tungsten film 6, the titanium nitride film 5, the polycrystalline silicon film 4, and the gate oxide film 3 are simultaneously patterned to form a gate electrode 7 using a resist (not shown) as a mask.
In the next, as illustrated in FIG. 12b, after forming side walls 8 on both sides of the gate electrode 7, BF2 is implanted in source/drain areas of the silicon substrate on both sides of the side walls 8 to form a p-type impurity diffusing layer 9, and is subjected to annealing at 800 through 1,000xc2x0 C. for activation.
In the next, as illustrated in FIG. 12c, an inter-layer insulating film 10 made of an SiN film, a PSG film, and a BPSG film is formed on an entire surface. Thereafter, when the PSG film and/or the BPSG film are used, a thermal treatment at 800 through 1,000xc2x0 C. is performed. This thermal treatment is an indispensable step because a quality of the inter-layer insulating film 10 is improved and planarized.
In the next, as illustrated in FIG. 12d, a contact hole 11 is opened at a predetermined position on the gate electrode 7 and the impurity diffusing layer 9. Further, there is a case that BF2 being an impurity of a type same as that of the impurity diffusing layer 9 is implanted in the semiconductor substrate from an opening portion of the contact hole 11, and the impurity is diffused by a thermal treatment at 800 through 1,000xc2x0 C.
Finally, as illustrated in FIG. 13, a metallic wire 12 made of aluminum and so on is formed, whereby a transistor having the gate electrode 7, fabricated by the tungsten film 6, the titanium nitride 5 being the reaction preventing film, and the polycrystalline silicon film 4, is completed.
The method of producing the conventional p-type MOS transistor using the polymetal wiring as the gate electrode wiring is as described. As illustrated in FIGS. 12b, 12c, and 12d, the impurity diffusing layer 9 is activated as described, wherein the thermal treatment process at 800 through 1,000xc2x0 C. is indispensable in order to improve the quality of the inter-layer insulating film 10 and planarizing the inter-layer insulating film 10.
Further, in the method of producing the conventional p-type MOS transistor, fluorine is taken in the polymetal wiring film in the following steps of the production.
(1) As illustrated in FIG. 11c, fluorine contained in the BF2 implanted in the polycrystalline silicon film 4 for forming the gate wiring of a p-type.
(2) As illustrated in FIG. 11e, fluorine contained in the tungsten hexafluoride used at time of forming the tungsten film 6 by the CVD method.
(3) As illustrated in FIGS. 12b and 12d, fluorine contained in BF2 implanted in the silicon substrate 1 and the tungsten film 6 at time of ion-implanting BF2 for forming the p-type impurity diffusing layer 9.
By the thermal treatment of fluorine taken in the polymetal wiring film, fluorine diffuses toward an interface between the polycrystalline silicon film 4 and the tungsten film 6 of the polymetal wiring, whereby a contact between the polycrystalline silicon film 4 and the tungsten film 6 is deteriorated. As a result, there is a problem that the polycrystalline silicon film 4 and the tungsten film 6 are separated at an interface therebetween during or after the thermal treatment or by stresses of the inter-layer insulating film 10 and of a film of metallic wiring 12.
Further, fluorine in the polymetal wiring diffuses and reaches the gate oxide film 3 by the thermal treatment, whereby an effective capacitance of the gate oxide film 3 increases. As a result, the effective film thickness of the gate oxide film is larger than a designed value, whereby there is a problem that a property of a transistor is deteriorated.
The present invention is provided to solve the above-mentioned problems inherent in the conventional techniques, and to provide a method of producing a semiconductor device having a polymetal wiring structure, by which a content of fluorine can be reduced, a film separation is prevented, and a preferable transistor property is obtainable.
According to a first aspect of the present invention, there is provided a method of producing a semiconductor device, wherein a tungsten film is formed by a sputtering method, and a content of fluorine in a target, used in the sputtering method, is 10 ppm or less.
According to a second aspect of the present invention, there is provided a method of producing a semiconductor device, wherein a tungsten film is formed by a sputtering method, and a temperature of a silicon substrate, formed by the sputtering method, is maintained to be 200xc2x0 C. or more.
According to a third aspect of the present invention, there is provided a method of producing a semiconductor device comprising a step of annealing the semiconductor device at 600xc2x0 C. or more after ion-implanting BF2 in a polycrystalline silicon film and before forming a reaction preventing film.
According to a fourth aspect of the present invention, there is provided a method of producing a semiconductor device, wherein a step of annealing is conducted in a vacuum for a reactive atmosphere for fluorine.
According to a fifth aspect of the present invention, there is provided a method of producing a semiconductor device comprising steps of sequentially forming a gate oxide film, a polycrystalline silicon film, a reaction preventing film, and a tungsten film on a silicon substrate; forming a silicon nitride film on the tungsten film; patterning the silicon nitride film; simultaneously patterning the gate oxide film, the polycrystalline silicon film, the reaction preventing film, and the tungsten film using the patterned silicon nitride film as a mask to form a gate electrode; and implanting p-type ions containing fluorine in the silicon substrate using the patterned silicon nitride film and the gate electrode as a mask to form an impurity diffusing layer.